There is an ever increasing need for single voltage source, multiple output voltage converters. Hence, there are a variety of methods in the prior art that treat this as a single input, multiple output (SIMO) problem by decomposing the system into multiple single-input single-output (SISO) systems. These can involve various hardware configurations or can involve manipulating switching times in each switching period, but all of these essentially depend on applying standard single input, single output (SISO) control methods such as PID in some way.
Operational equilibrium points and corresponding duty ratios D, for a SISO system with common voltage converters are known. For example, the output voltage of a boost voltage converter is 1/(1−D) times the input voltage. The output voltage of a buck-boost voltage converter is D/(1−D) times the input voltage.
There are several nonlinear control methods to deal directly with the nonlinear state equations for the SISO boost and buck-boost converters. If leading edge modulation is used to derive the output state equations, and if the zero dynamics are asymptotically stable, then input-output linearization techniques can be employed to stabilize the system and perform the desired output tracking while allowing the system to remain linear at all operating points.
As to prior art, Cuk et al. in U.S. Pat. No. 5,442,534 discloses an isolated, capacitive idling, Cuk switching mode converter with multiple output converters and PWM feedback control of duty cycle of switches in the converter. Cuk et al. discloses a converter with a primary side and multiple secondary sides separated by a transformer, the primary side controlled by one feedback loop and the secondary sides controlled by independent feedback loops. However, Cuk et al., does not disclose a single controller for the multiple output converters, instead relying on two or more separate and independent nonisolated feedback loops to independently control the duty cycle of each switch in the converter.
U.S. Pat. No. 7,851,941 to Walley discloses a method and system for multiple output capacitive buck-boost converter. Walley discloses a switch array controlled by a single state machine controller with integrated instructions for power control. The switch array is connected by two external switches to two output voltages having IN sensors which are connected to the state machine controller. However, Walley does not disclose a controller programmed for boost and buck-boost conversion utilizing leading edge modulation with attention to the zero dynamics or input-output linearization. Furthermore, Walley does not address stability of the multiple output capacitive buck-boost converter.
U.S. Patent Application No. 2010/0164282 to Tseng et al., discloses a single-input multi-output switching regulator converting an input voltage to a first output voltage at a first node and a second output voltage at a second node, the first output voltage and second output voltage being generated by two capacitive circuits integrated with an inductor and a set of switching elements. Tseng et al. further discloses a pair of settable switches providing a selectable set of interconnections between the two capacitive circuits and the input voltage, providing a selectable set of output voltages at the first and second nodes. Tseng et al. does not disclose any apparatus or methodology for controlling the duty cycles of the switching elements and does not address stability of the multiple output switching regulator.
In actuality, the single voltage source, multiple-output voltage converter has inherent coupling between the voltage outputs. What is needed is an application of a full multiple-input multiple-output theory to the design and control of voltage converters to properly account for this coupling.